Screen grid metal tube



J. E. BEGGS Inventor James E. E ggf9 bg His Atbovheg.

SCREEN GRID METAL TUBE Original Filed Sept. l. y1.93

@epm M? E937.

Patented Sept. 14, `193,7

UNITED STATES PATENT OFFICE soaEEN cmo METAL TUBE James E. Boggs,Scotia, N. Y., assignor to General Electric Company, a corporation ofNew York Original application September 1, 1934, Serial 8 Claims.

The present invention relates to electron discharge apparatus, and moreparticularly to thermionic devices employing metal envelopes.

This application is a division of my application duction basis and inwhich the metal container serves the function of one of the screenelectrodes. Other objects and features will be apparent as thespeciilcation is perused in connection with the accompanying drawingv inwhich Fig. 1 is a view, partly in section, of a thermionic deviceimproved in accordance with the present invention and embodying theimproved screen electrode; Fig. 2 is a view of the tube shown in Fig. 1but with the envelope removed and the anode cut away to show theinterior electrodes; Fig. 3 is an enlarged sectional view of a preferredform of cathode employed in the tube shown in Figs. 1 and 2; Fig. 4 isan enlarged fragmentary sectional view oi' a typical seal employed inthe tube shown in Figs. 1 and 2; Fig. 5 is a modified form of metal tubeemploying a screen electrode, while Fig. 6 is a view similar to Fig. 5except that the upper seal and the metal seal-off are shown in sectionand the anode is cut away to show the interior electrode structure moreclearly.

Referring more particularly to Fig. l, numeral i designates a cylinderconsisting of any readily workable, inexpensive metal such as iron,nickel, etc., which is closed at the top (as shown) by a metal headermember 2 and at the bottom by a metal header member 3. These headersconveniently take the form of a reentrant cylindrical member fittingsnugly within the interior of the envelope l to which they may besecured in any suitable and well-known manner, as by welding.

l'lhe interior assembly of the tube, as illustrated more clearly in Fig.2, takes the form of a four-electrode device having a cathode d, anelectrostatic control grid 5, a screen grid t, all preferably ofcylindrical configuration and surrounding one another. While anysuitable form of cathode may -be used, I prefer to employ an indirectlyheated cathode of the type shown in Fig. 3. In this iigure, numeral 8designates a tungsten heater which may take the form of a hairpin,insulatingly mounted Within the cylinder 4 which is preferably of nickeland constitutes the cathode proper, The cylinder t advan- Divided andthis application December 17, 1936, Serial No. 116,398

(ci. 25o-21.5)

tageously may be coated with electronically active material S such asbarium and strontium oxide obtained initially from the carbonate as iswell known in the art. Leads I@ may be taken from both ends of theheater and a lead Il connected to the lower end (as shown) oi thecathode cylinder.

The gridV or electrostatic control member 5 may consist of a circularwire helix, woundon a pair of metal uprights l2, one of which, theextreme right-hand member as shown, is extended and joined to aleading-in conductor I3 taken out through the upper end of the tube. Thescreen grid may also consist of a wire helix but of larger diameter thanthe control grid, and wound on a pair of metal uprights lll. One ofthese uprights may be extended to make suitable connection with thecontainer by means of a transverse conductor l5 as will be explainedhereinafter.

The anode 'l may consist of a metal cylinder, preferably of nickel, andprovided at diametral positions with a pair of rod uprights I6, one ciwhich, the left-hand rod as shown, being extended and connected to aleading-ln conductor il.

The electrode structure as a whole is mounted on a frame constituted ofa pair of metal uprights il@ which are secured by flanged metal collars2l to the upper and lower headers 2, 3. It is apparent that the uprlghts2G serve to maintain the proper spacing between the headers and togetherwith the latter constitute a rigid rectangular frame.

The control grid uprights l2 and the screen 1.

grid uprights lil are spaced .and maintained in proper position by meansoi' a pair of disks 22, of insulating material such as mica, whichcontain openings for snugly receiving the uprights. On the upper side ofthe upper disk 22 and the lower side of the lower disk 22, there is apair of disks 23, also of mica but of larger diameter than the disk 22.The disks 23 have openings about the periphery to receive the anodeuprights i6. The upper disk 23 is of a diametral size such as to iltsnugly Within the metal cap member 2d, the purpose of which will beexplained hereinafter. The cap 24 is provided with a slot (not shown butindicated by the lack of cross-sectional lines along the flattenedportion of the mernber), sufliciently large to permit the control gridleading-in conductor and the cathode to pass through without touching.The frame members 20 also pass through the slot and are rigidly securedto the cap member 24 by angle pieces 25.

In order to maintain the mica disks 22 and 2l perfectly flat, i. e. toprevent warp, and in order to oil'er more rigidity to the supportingframework, I have provided at each end of the electrode structure,transverse metal bars 26 which are respectively secured to each pair ofmica disks 22, 2l, for example by riveting and also secured as bywelding, to the frame uprights 20. Each of these bars is provided with atransverse slot corresponding to the slot in the cap 2l in order topermit the upper ends of the control 4grid uprights i2, also the upperend of the cathode cylinder 4 and the lower ends of the screen griduprights il, and thelower end of the cathode l, to pass through withoutcontacting with the bars.

The control grid leading-in conductor I3 is taken out through the upperheader 2 by means of an improved seal shown more completely in Fig. 4which constitutes the subject matter of my application Serial No.744,165, filed September 15, 1934 and entitled Glass-to-metal seals, andis disclosed and claimed in broader scope in the Elder and Gableapplication Serial No. 746,808, filed October 4, 1934, and entitledElectricdischarge devices and seals therefor. These applications areassigned to the same assignee as the present invention.

Leading-in conductor I1 of the anode, conductor Ii of the cathode, andconductors I0 of the heater member are taken out through the oppositeheader 3, also by means of improved seals. There is no leading-inconductor for the screen grid 6 because the conductor i5 between thescreen grid and frame upright 20 connects the screen grid to the headers2, l, and thus to the envelope i.

The flattened portion of the header member is provided with an openingat the position where it is desired to pass the leading-in conductorthrough. Secured to the header at the opening, for example, by welding,there is a metal eyelet 28 which is provided at one end (at the bottomas shown) with an outwardly extending flange in order to be securedeither to the under side or the upper side of the header member. Acylinder 29 of glass or other vitreous material within the eyelet maysupport and insulate any one of the leading-in conductors from theeyelet and hence from the header member. A hermetic seal is formedbetween the conductor, the glass and the eyelet, preferably by means ofa gas flame which is directed at the proper position on the eyelet afterthe conductor and glass have been assembled in the eyelet. Theseal,'including the conductor, glass and eyelet members, is completed asa unit, apart from the header member after which the eyelet isvsecuredto the header.

In order to insure an absolutely vacuum-tight seal between the glass 29and the eyelet 20, these members should preferably have substantiallythe same thermal expansion characteristic over the entire temperaturerange between 0 C. and the softening temperature of the glass. Thus nostress or strain is introduced at the various joints during fabricationof the seal or during any subsequent heat treatment of the tube whichcontains the seal. While various metals and glasses may be employed forthis purpose, the freedom from stress and strain at the seal beingdependent upon the amount of materials involved and the respectivedifferences of thermal expansion at the various temperatures reachedduring the manufacture of the tube, I prefer to employ materials whichhave been disclosed and claimed in the Burger and Hull applicationSerial No.

2 a,oos,sos

705,250, nled January 4, 1934 and entitled Glassto-metal seals, assignedto the sameassignee as the vpresent invention. This application hasmatured into Patent 2,071,196. As pointed out in the Burger and Hullpatent, a metal which may be advantageously employed for a substantiallystrain-free seal, regardless of the amount of metal and glass used orregardless of the temperatures reached during manufacture, consistsapproximately of 18% cobalt (Co), 28% nickel (Ni), 54% iron (Fe), andthe glass in this case may have the following approximate composition:65% silica (SiOs), 23% boric oxide (B201), 7% sodium oxide (NazO) and 5%aluminum oxide (A1201). v

As stated hereinbefore, when the eyelet is welded to the fiat portion ofthe header member, either on the under or the upper side thereof, andwhen the glass member 2l and the metal member 28 are of the propermaterials, the leading-in conductor is carried through the metal headerin an insulating manner and is hermetically sealed. A sumcient number ofthese seals are provided to accommodate the variousleading-in-conductors. e

In addition to these seals, the lower header member 3 carries a seal-oi!tube 20, constituted of a readily workable metal such as steel, which ishermetically secured to the header member in any suitable andwell-knownl manner, for example by welding or copper brazing in ahydrogen furnace. An excess of tubulation III is provided, theadditional length being cut on during the seal-off process as will bedescribed presently.

When the leading-in conductor seals and the metal seal-off have beensecured to the proper headers. and the electrode assembly, including theframe uprights 20, has been assembled and secured between the headers,connections are made between the various leading-in conductors and theirrespective electrodes, as has been explained hereinbefore. Thus themetal headers and the electrode structure together with the supportingframework and elements, constitute the entire structure contained withinthe envelope i. The structure as a whole is extremely rigid in view ofthe support offered by the header members and the frame uprights 20.I'he feature of providing a pair of metal headers connected together bya rigid framework which supports the electrodes and constitutes acomplete assembly unit is disclosed and claimed in my application SerialNo. 742,407 flled September 1, 1934 entitled Electrode structures formetal tubes and assigned to the same assignee as the present invention.This application has matured into United States Letters Patent No.2,056,035.

The next step in the process of manufacture is to secure the headermembers and associated elements to the envelope. 'I'he headers are ofsuch a diameter as to ilt snugly within the envelope I, and are sospaced that their outer edges align themselves with the edges of thecylinder i. The entire unit may be slipped into place and the headerswelded or otherwise permanently and metallically secured to theenvelope. The tube is then placed on an exhaust system and the interiorof the envelope evacuated through the tubulation 30. During this time,the metal envelope is heated by high frequency or by a gas orelectrically operated oven, to a temperature. for example, ofapproximately 700 C., sufficiently high to remove the occluded gasesfrom the envelope material and yet not high enough to cause the glassmembers 29 to `melt in Fig. 6 and comprises an indirectly heated orotherwise to cause damage to the non-metallic elements. The evacuationshould preferably be cor. lucted at a fast rate, after which the tube isgettered in any suitable and well-known manner.

When a sufilciently high vacuum has been obtained, the tube is sealedfrom the pump by closing the tubulation 30 in any suitable manner, forexample by simultaneousiycollapsing the tubulation and welding the sidesthereof. After the weld has been made. the surplus length of tubulationmay be snipped of! by cutting pliers, whereupon the tube is removed fromthe evacuating system. A base may be provided, ii desired, and thevarious leading-in conductors colinected to the usual contact pins.

As stated hereinbefore, the screen grid 8 is connected to the envelopethrough the short transverse conductor I5 and the frame uprightsconsequently, the metal envelope serves not only as a rugged containerfor the electrodes but also as a part of the screening system forintercepting electrostatic lines of force which tend to pass between thecontrol grid and the inner or outer surfaces of the plate. While I amawarethat screen grids having a portion interposed between the controlgrid and the anode and another portion positioned on the opposite sideof the anode have been employed heretofore in tubes, it should be notedthat in the case of the prior tubes, an outer screen electrode isutilized in addition to the envelope. However, in accordance with thepresent invention, the screen electrode has been combined with theenvelope so that one less element is necessary under these conditions.Furthermore, by connecting the inner screen electrode with the metalenvelope, an external connection may be effectively made with the innerscreen electrode by simply making contact with the envelope, thuseliminating the usual leading-in conductor for the inner screenelectrode.

The cap 24 is provided in order more effectively to shield the anodefrom the control member and more particularly for'the purpose o'fintercepting the electrostatic lines of force which pass between theleading-in conductor I3 of the control grid and the outer upper surfaceof the anode. It ls apparent that any lin'e drawn between the conductorI3 and the exterior surface of the anode will be intercepted either bythe cap member 2C or by the envelope I or by both.

Figs. .5 and 6 show a modified type of screen grid tube, illustrated inthe form of a pentode. The parts in these figures which correspond tothe elements shown and described in connection with Figs. l, 2, 3 and 4have been given similar reference characters. It will be noted that thetube shown in Figs. 5 and 6 employs only one metal header, namely theelement 3, because the upper end of the envelope 3| ls closed by aportion integral with the envelope and' produced by a deep-drawingprocess. member consists of a reentrant wall portion 32 which terminatesin a rectilinear wall portion 33 forming a closed compartment 34. Aledge 35 is formed vwithin this compartment and resting against theledge there is a mica disk 3 8, the function of which is to support theupper ends of the electrodes. For this purpose, the disk 36 is providedwith openings snugly to receive the various electrode uprights and theupper end of the cathode l.

The electrode structure is shown more clearly The upper closure cathode8 which may be similar to that shown and described in connection withFig. 3, a helical control grid 5, a helical screen grid B, an anode 1and In addition, a secondary emission suppression grid 31, Vtermed asuppressor grid," positioned between the anode and the screen grid. Thevarious grids 5'. B and 31 are wound around their respective uprightsI2, i4 and 38, these uprights fitting snugly at the top, in openingsprovided in the mica disk 38 and having their lower ends supportedwithin openings provided in a mica disk 38. The disk 38 is containedwithin a plate member 40 of circular configuration and provided at theupper edge with a flange in order to receive the disk 39. The platemember 40 is provided at the lower edge with a metalbar 4I which carriesa longitudinal slot of sufficient size so that the various leading-inconductors for the electrodes may pass through without touching.

The plate member l0-is supported from the header member 3 by means of apair of rigid up- 'rights 82, at diametral positions, which are securedto the header by means of hanged metal members 2l. A leading-inconductor I3 for the control member is taken out through the top of theenvelope and may constitute an extension of one of the control griduprights. The cathode 4 is connected to the longitudinal bar 42 by meansof a conductor 43 and the suppressor grid is also effectively connectedto the same bar by means of the conductor M. It is apparent that thecathode and the suppressor 'grid are effectively connected to theenvelope 3i through the uprights 42 and the header member 3.

'Leading-in conductors 45, 48 and 41 are provided respectively for theanode 1, the heater 8 and the screen grid 6. These conductors areinsulatingly taken through the header by means of improved seals, anexample oi which is shown in Fig. 4 and was described in connection withthat ligure. It will be understood that any other suitable form of sealmay be employed for this purpose. The leading-in conductor I3 at the topof the envelope preferably employs a seal having a long extended glassportion 48 provided with a groove between the glass and the conductor,also between the glass and the eyelet 28 so as to offer increasedleakage paths between the conductor and the eyelet. As in the case ofthe seal shown in Fig. 4, the seal shown at the upper end of Fig. 6 isalso disclosed and claimed in my patent application Serial No. 744,165.

As stated in the application, Serial No. 744,165, the improved seal notonly insulatingly carries the leading-in conductor I3 through the metalclosure member but also serves as a support member for the mica disk 36.I! desired, a seal similar to the one shown in Fig. 4 may be employedfor this purpose and a spacer substituted for the portion d8 between theupper surface of the disk 36 and the lower surface of the attened endportion of the envelope tI. It is apparent that in view of the supportprovided by the glass extension member I8 and the ledge 35, the micamember 36 is very rigidly held in position at the upper end of theenvelope.

In addition to the seals 28 and the support members 2l, the headermember 3 carries a metal seal-olf tube 38 which is hermetically sealedto the header as was explained in connection with Figs. i and 2. The endof the seal-off tube remote from the envelope is hermetically closed,preferably by welding, after the exhaust and gettering treatments havebeen completed. In order 4 aoeasos to getter a tube of this type, theremay be provided a gettering material indicated by reference characterIl, which may consist of a piece of magnesium pressed tightly betweenthe wall I2 and the upper end of the envelope ll, the getter being insuch a positionthat it may be vaporized readily by torching the upperend of the metal envelope adjacent the getter. In order to prevent thegetter vapor from migrating to undesired positions within the tube, itmay be desirable to provide a metal bame l0 provided with openings 6lfor evacuation land gettering purposes. 'I'he baille is of such adiameter as to nt snugly within the envelope 3| and has an opening atthe center which mayfit tightly about the uprights 38 of the suppressorgrid. l

It is apparent in Figs. 5 and 6 that the cathode and suppressor grid areconnected together and are maintained at the same potential as theenvelope. On the other hand, the screen grid l is insulated from theenvelope and a leading-in. conductor 41 is brought out from this grid sov that various potentials may be applied thereto with respect to thecathode. It is obvious that these potentials may be predetermined inorder to permit the screen grid to intercept and neutralize the effectof the electrostatic lines of force which normally pass between thecontrol grid and the anode. Inasmuch as the envelope Il is at the samepotential as the cathode, it also will serve as a part of the screeningsystem and will intercept the electrostatic lines of forcey which tendto move between the control grid and the exterior surface of the anode.'Ihe configuration of the upper end of the envelope 3| is such thattheelectrostatic lines of force between the grid leading-in conductor i3and the exterior surface of the anode are eifectively intercepted by themetal closure. It is apparent that this end of the 4o envelope performsthe function of not only serving as a closure for the envelope but alsotakes on the role of a screen member which is similar in function to thecap member 24 shown in Figs. 1 and 2. Accordingly, the improved form ofenvelope eliminates the necessity for the cap member and to that extentrepresents a more simple construction.

The tube shown in Figs. 5 and 6 oii'ers the advantage that no leading-inconductor is necessary for the cathode or suppressor grid, since thesemembers are maintained at the same potential as the envelope to which aconnection may be readily made in order to connect with the respectiveelements. Inasmuch as the anode is physically independent of theremaining electrodes and is n'ot supported by a dielectric member incommon with the other electrodes, greater screening edects may berealized in a tube of the character shown in Fig. 6 than in the tubeconstruction shown in Fig. 2. However, it will also be understood inthis connection that if desired, the internal elements of the tube shownin Fig. 2 may be supported in such a manner as to employ less dielectricmaterial than is illustrated and thus realize enhanced screeningeffects.

'I'ubes improved in accordance with my invention in which the metalcontainer serves as part of the screening or shielding system arereadily adapted to external shielding, since the container or envelopemay constitute an integral part of the shielding apparatus which isprovided in connection with the radio receiver set of which the improvedtube may constitute one amplincation or detection stage. An example ofthe enhanced 15 external shielding onered by the metal container,

is when the tubes are clamped through a shield partition mountedapproximately midway of the length of the envelope in such a manner thatthe plate lead is in one compartment provided by the partition ncf thegrid lead is in another 5 compartment provided by the same partition.Obviously, since the partition and the metal envelope are effectivelygrounded or at least connected to cathode potential, no electrostaticlines of force, regardless of their curvature or length, lo can possiblyextend between the grid and plate leads.

In view of the foregoing,` it is apparent that I have disclosed a screengridtube which 'is readily adapted to be manufactured on a quantityl 15production basis and which lends itself to any number of grid electrodesby simply changing .the number of openings and distance between openingsin the respective mica disks 36 and 39, with proper provision in theheader member I 20 for insulatingly taking out leading-in conductorsfrom the various electrodes. The metal container Il in connection withthe upper closure member oii'ers the most effective shielding for thecontained electrodes so that in a tube of this 25 character, there is notendency for the production of undesired high frequency oscillations byreason of interelectrode capacity. As stated hereinbefore, considerablesaving is offered by a metal tube of this type in providing enhanced 30screening effect without necessitating additional electrodes andleading-in conductors, since the metal container serves the dualfunction of an envelope as well as a screen electrode.

Some of the screening features shown herein 36 are disclosed and broadlyclaimed in the Livingston application Serial No. 704,503, filed December29, 1933, entitled E'lectrostatically con-l trolled arc dischargedevices, assigned tothe same assignee as the present invention. This 40application has matured into Patent 2,044,618.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An electric discharge device comprising a metal envelope containing acathode, an anode, 45 I and a control grid, said envelope being providedwith a metal end portion formed integrally withA the envelope where thecontrol grid leading-in conductor passes through the envelope, and meansincluding said envelope and the metal end 50 portion for interceptingsubstantially all of the electrostatic lines of force extending betweenthe exterior surface of the anode and said leading-in conductor.

2. An electric discharge device comprising a 55 metal envelope andcontaining a cathode, an anode, a control grid, and a screening grid,leading-in conductors for the anode, control grid and screening grid.said envelope being connected to the cathode and provided with a metalend por- 60 tion formed integrally with the envelope where the controlgrid leading-in conductor passes through the envelope, said envelope endportion enectively'intercepting substantially all electro# static linesof force extending from the anode 55 toward the control grid leading-inconductor.

3. An electric discharge device comprising a metal envelope containing acathode, an anode. and a control grid, said envelope being provided witha metal end portion formed integrally with 70 the envelope where thecontrol grid leading-in conductor passes through the envelope. means forintercepting substantially all of the electrostatic lines of forceextending between the anode and the control grid, said interceptingmeans consisting in part of said envelope and the metal end portion, andin part of a screening element interposed between the anode and thecontrol grid.

4. An electric discharge device comprising a hollow metal cylinderclosed at one end by a metal header hermetically secured thereto'and atthe other end by an integral reentrant portion.

at the other end by an integral reentrant portion which terminates in achamber extending rec- 20 tilinearly with respect to said cylinder, aplurality oi' electrodes in said cylinder, means for insulatinglymounting the electrode structure, at one end from said header and at theother end from the wall portion which forms said chamber, 25 leading-inconductors for the electrodes hermetically sealed in said header andinsulated therefrom.

6. An electric discharge device comprising a hollow metal cylinderclosed at one end by a. 30 metal header hermetically secured thereto andat the other end by an integral reentrant portion which terminates in achamber extending rectilinearly with respect to said cylinder, a gettermaterial in said chamber, a plurality of electrodes 35 in said cylinder,means for insulatingly mounts ing the electrode structure, at one endfrom said header and at the other end from the wall portion which formssaid chamber, leading-in conductors for the electrodes hermeticallysealed in said header and insulated therefrom.

7. An electric discharge device comprising a hollow metal cylinderclosed at one end bya metal header hermetically sealed thereto and atthe other end by an integral reentrant portion which terminates in achamber extending rectilinearly with respect to said cylinder, a gettermaterial in said chamber, a plurality of electrodes in said cylinder,means for preventing the vapor of said getter material when ashed fromstriking said electrodes, and means for insulatingly mounting theelectrode structure, at one end from said header and at the other endfrom the wall portion which forms said chamber, leadingin conductors forthe electrodes hermetically sealed in said header and insulatedtherefrom.

8. An electric discharge device comprising a hollow metal cylinderclosed at one end by a metal header hermetically sealed thereto and atthe other end by an integral reentrant portion which terminates in achamber extending rectilinearly with respect to said cylinder, a gettermaterial in said chamber, a plurality of electrodes in said cylinder,means including a shield member interposed between the getter materialand the electrodes for preventing the vapor of said getter material whenashed from striking said electrodes, and means for insulatingly mountingthe electrode structure, at one end from said header and at the otherend from the wall portion which forms said chamber, leading-inconductors for the electrodes hermetically sealed in said header andinsulated therefrom.

JAMES E. BEGGS.

